The bright spots were far and few between during the 49ers’ embarrassing 34-0 defeat to the Broncos earlier today. The team’s signal callers struggled in particular, with the four quarterbacks on the roster failing to produce even a single touchdown drive, and combining to produce three points in two preseason games thus far.

Of the four quarterbacks on the roster, only starter Colin Kaepernick‘s job is secure, and hopefully for the team he will stay healthy and his backups will never see any meaningful action. Even still, there is concern over the uncertainty of the three players vying to be the number two passer on the depth chart.

Blaine Gabbert was thought to have the inside track, after the 49ers traded a sixth round pick to the Jaguars to acquire his services. However, through two preseason games he has completed only 11/27 passes for 60 yards, throwing two interceptions in the process. His performances have left his spot on the team in doubt.

At the same time, fellow backups Josh Johnson and McLeod Bethel-Thompson have failed to impress themselves. Bethel-Thompson has thrown two interceptions himself, and while Johnson escaped the preseason opener without a turnover, he lost a fumble today against the Broncos.

Head coach Jim Harbaugh is unhappy with the amount of turnovers he is seeing from the group, noting that turnovers will be the deciding factor on who gets the nod in the event Kaepernick should need to be replaced, writes Matt Maiocco of CSNBayArea.com.

“In terms of a backup quarterback, it’s as simple as who doesn’t turn the ball over,” Harbaugh said. “They’re turning the ball over. All of them have. There’s nobody to elevate. Whoever doesn’t turn the ball over will be the backup quarterback.”

Harbaugh still shot down the idea that the team would look outside the organization for a suitable backup.

One quarterback who could provide an upgrade over the current backups is Christian Ponder, writes Daniel Jeremiah of NFL.com (via Twitter). Ponder has fallen out of favor with the Vikings, as Matt Cassel and Teddy Bridgewater are currently battling for the starting job in Minnesota.

The team will of course like to get 16 games out of their starter, but in today’s NFL, a weak backup quarterback can take a contender to a bottom dweller in a hurry.